The present invention relates to a packing container for pressurized contents, having an outer casing and a liquid-tight inner container. The invention also relates to a method for manufacturing a packaging container for pressurized contents, comprising an outer casing and a liquid-tight inner container.
Packing containers for pressurized contents, such as beer and carbonated refreshing beverages, exist in a great number of forms. One of the more common types is a 45 cl can which is manufactured from aluminium or a combination of sheet metal and aluminium. In the manufacture of such a container a shell wall formed by deep-drawing or by some other method is provided with one or more end walls which are joined to the shell wall by seaming. One end wall has a pre-manufactured opening arrangement.
Known types of cans are relatively expensive to manufacture and it is therefore a general objective to produce a packing container which, functions in a satisfactory manner and can be manufactured at a lower cost.
One suggestion in this respect is to make the packing container of different and cheaper material. However, up to now no packing container has been proposed which was of a cheaper design and at the same time had the strength and tightness of the conventional can. This is due to the fact that the cheaper materials which are available have different, and very frequently inferior, characteristics when it comes to withstanding the internal pressure in the packing container caused by its contents and to preventing gas exchange between the packing container and the surroundings.
These disadvantages can be avoided in the manufacture of packing containers by the combination of different types of material, so that the properties of each type of material are utilized and they are made to co-operate in the best possible manner. In a known type of a package an inner plastic container is thus provided which is surrounded by an outer, relatively thick paper casing which absorbs the pressure originating from the contents. The ends of the container, however, are not covered by the casing and have to be made, therefore, of considerably thicker material. The ends are given a shape which is appropriate in respect of the pressure loading but which is impractical from a user's point of view. This container also lacks a satisfactory gastight layer which has a negative effect on the keeping quality of the packed contents.
It is an object of the present invention to produce a packing container of the type mentioned in which different material layers are utilized in an optimum manner in respect of each of the different functions: strength, liquid-tightness and gas-tightness.
It is a further object of the present invention to produce a packing container wherein the consumption of material is minimized and is adapted so that the packing container obtains maximum strength and stability at the lower possible expense.
It is also an object of the present invention to produce a packing container wherein gas exchange between the inside and outside of the packing container is prevented at the same time as the presence of air is avoided in the packing container which may be harmful to the contents.
These and other objects have been achieved in accordance with the invention in a packing container for pressurized contents having an outer casing and a liquid-tight inner container. The outer casing includes a layer of gastight material which completely encloses the inner container and the inner container is manufactured from a flexible material which through the pressure originating from the contents is pressed against the outer casing.
By placing the gastight layer into the outer casing which has a stable shape and is almost unaffected by the internal pressure of the packing container, the tensile stresses in the gastight layer are avoided. This eliminates the problem of cracking, normally encountered in the earlier types of packages, which precluded the use of certain types of gastight layer, e.g. aluminium foil. Such the liquid-tight layer is manufactured from thin, flexible material which through the pressure of the contents is flattened against the inside of the outer casing and subsequently is not subjected to any further loads, no appreciable demands with regard to strength are made on it, so that the gastight as well as the liquid-tight layer may be made very thin.
As the liquid-tight layer is not gastight, it means that not only the space present inside the inner container which is not filled with contents, but also any space between the container and the casing, can be filled with gas originating from the contents which in contrast to the oxygen in the air is not harmful to the filled product.
It is a further object of the present invention to provide a method of manufacture of a packing container for pressurized contents, this method being adapted so that it can be carried out by means of automatic manufacturing and filling machines.
It is a further object of the present invention to provide a method of manufacture which makes possible the consecutive manufacture and filling of a packing container without any surrounding air being packed together with the contents or making contact with them in some other manner.
These and other objects have been achieved in accordance with the invention in a method for the manufacturing of a packing container for pressurized contents having an outer casing and a liquid-tight inner container. The inner container and its contents are introduced into the outer casing, the outer casing being made to enclose the inner container in a non-gastight manner and the contents are made to give off gas so that any air remaining in the outer casing is forced out whereupon the outer casing is sealed in a gastight manner.
The method in accordance with the invention makes use of the gas developed by the contents so as to induce the inner container to lie closely against the outer casing and to force out the air from the outer casing prior to being sealed in an airtight manner. The inventive method results in the inner casing which can be made of a very flexible and expandable plastic material being brought to lie particularly closely against the outer casing so that the air space is eliminated and the container obtains the required mechanical support from the outer casing.